EP 0 889 265 A1 discloses a piston seal including an inside sealing lip and an outside sealing lip, with the inside sealing lip being stressed dynamically, while the outside sealing lip is stressed statically. The outward end of the outside sealing lip projects in an axial direction from the outward end of the inside sealing lip. A bead that is used as a support and makes catch at the piston in a radial direction reinforces the prior art sealing collar.
DE 198 12 041 A1 discloses a sealing element for sealing two coaxial surfaces displaceable relative to each other in an axial direction. Said sealing collar comprises an outside and an inside sealing lip abutting radially on the surfaces being sealed. To increase the force by which the sealing lips bear against the surfaces, the sealing lips are interconnected by radial webs.
To enhance the sealing effect it is generally desirable to make the ends of the sealing lips sufficiently elastical because friction can be reduced and the sealing effect can be enhanced hereby. This means that the sealing lips will have a relatively long and small design. However, as the inside sealing lip with its free end reaches into the area of the boundary between the cylinder and the piston and these boundaries move relative each other, there is the risk that the end of the sealing lip is squeezed in the slot between cylinder and piston. This can occur in particular when there is a major pressure gradient between the rear side of the sealing collar and the sides of the sealing collar associated with the sealing lips.
Remedy is taken in providing the sealing lip which is stressed only statically and disposed on the bottom of the groove for accommodating the sealing collar with a relatively stiff design and additionally making the end of this sealing lip project axially over the end of the dynamically stressed sealing lip. The result is a construction similar to the design illustrated in the above-mentioned European patent specification. It is, however, disadvantageous that such a stiff sealing lip provides a reduced sealing effect and does not lend itself to ease of mounting.